1. Field of the Invention
The present invention relates to a receiver of a display driving system, and more particularly, to a receiver having a clock recovery unit based on a delay locked loop, wherein a PLL (phase locked loop) structure is excluded and a clock recovery unit realized using only a DLL (delay locked loop) structure without using a separate oscillator for generating a conventional reference clock signal is employed so that a clock signal embedded between data signals having the same level and amplitude as the data signal can be recovered.
2. Description of the Related Art
In general, display devices include a timing controller which processes image data and generates a timing control signal so as to drive a panel for displaying the image data, and data drivers which drive the panel using the image data and the timing control signal transmitted from the timing controller.
Interfaces for transmitting image data to be displayed, between the timing controller and the data driver, include a multi-drop signaling interface, in which the data drivers share a data signal line and a clock signal line, a PPDS (point-to-point differential signaling) interface, in which data differential signals and clock differential signals are separately supplied to the respective data drivers, and an interface, in which data and clock signals are separated into multiple levels and data differential signals with the clock signals embedded therein are transmitted from the timing controller through independent signal lines to the data drivers.
The present applicant has proposed an interface in Korean Patent Application No. 10-2008-0102492, in which a single level signal with a clock signal embedded between data signals (LVDS data) to the same level is used and data and a clock signal are transmitted together by an independent single signal line so that the data and the clock signal can be recovered by a receiver.
In the interface for transmitting data differential signals with clock signals embedded therein to the data drivers by respective independent signal lines, a transmitter generates a transmission signal that corresponds to respective data bits and transits periodically. The periodic transition can occur by dummy bits that are inserted between data bits of a predetermined number. That is to say, the periodic transition occurs due to the fact that a portion immediately before and after the data bits to be transmitted has a value different from the data bits. In this case, since a receiver provided in the data driver cannot receive a separate clock signal, in order to receive the data differential signals with the embedded clock signals and recover original data, the clock signals embedded between the data signals should be recovered from the received differential signals.
Therefore, the receiver should be provided with a recovery circuit for recovering the clock signals, and it is the norm in the conventional art that such a clock recovery circuit is configured to have a phase locked loop (PLL) structure. That is to say, because a reference clock signal as a clock signal generated by oscillation inside the receiver is needed to recover the received data, it is the norm that the clock signal recovery unit is configured by the phase locked loop (PLL) which has an oscillator for generating the reference clock signal.
As is disclosed in Korean Patent No. 868299, a conventional receiver provided in the data driver includes a clock generation unit which is configured to generate a received clock signal from the periodic transition of a differential signal received through a signal line, and a sampler which is configured to sample the differential signal according to the received clock signal and recover data bits.
The clock generation unit includes a transition detecting circuit configured to output a signal corresponding to a time difference between the periodic transition of the received differential signal and the transition of a feedback clock signal, and an oscillator configured to change the phases of the feedback clock signal and the received clock signal in response to the signal outputted from the transition detecting circuit.
The transition detecting circuit is configured in such a manner that the oscillation frequency of the oscillator is determined by the clock signal inputted upon initial synchronization and the operation of a transition detector is interrupted or restarted in response to an enable signal when data is inputted thereafter. In this case, while the enable signal is generated by the clock signal inputted upon the initial synchronization, since there is no clock edge during a time interval excluding the interval of the enable signal, no influence is exerted on the generation of the received clock signal.
Therefore, the clock generation unit is configured in such a manner that only the rising edge or the falling edge of the received signal composed of the dummy bits is recognized as a transition during an interval in which the enable signal has a high logic level and is not recognized as a transition during an interval in which the enable signal has a low logic level, so that the frequency and the phase of the received clock signal generated by the oscillator deviate from the periodic transition by the dummy bits.
Thus, the conventional clock generation unit is configured based on the phase locked loop (PLL) structure having a characteristic that the feedback signal in the oscillator is inputted again to the oscillator after the initial synchronization to generate the enable signal.
However, the conventional clock generation unit configured based on the phase locked loop (PLL) structure has a problem in that jitter continuously accumulates in the phase lock loop (PLL) as an internal feedback loop.
Also, the conventional clock generation unit may be configured to have not only the characteristic of a delay locked loop (DLL) in that the received signal is directly inputted to the oscillator in the initial synchronization to generate the enable signal but also the characteristic of the phase locked loop (PLL) in that the feedback signal in the oscillator is inputted to the oscillator after the initial synchronization to generate the enable signal.
Nevertheless, the conventional clock generation unit, which is configured to operate by the delay locked loop (DLL) structure in the initial synchronization and by the phase lock loop (PLL) structure after the initial synchronization, has a problem in that the oscillation frequency and the phase are likely to be distorted due to the change of the loop during operation.
Further, since the enable signal is generated by the phase locked loop (PLL) structure after the initial synchronization, a problem is still caused in that jitter continuously accumulates in the phase locked loop (PLL) as an internal feedback loop.